Prostate cancer is one of the leading cancers diagnosed in men within the United States and is expected to affect 241,470 men of which 28,000 will die in 2012. See, e.g., Siegel R, Ward E, Brawley O, et al. Cancer statistics, 2011: the impact of eliminating socioeconomic and racial disparities on premature cancer deaths. CA Cancer J Clin; 61:212-236. One of the variety of treatment options includes radiation therapy.
Radiation therapy techniques include intensity modulated radiotherapy (IMRT) and image-guided radiotherapy (IGRT). Some IGRT systems, such as the Calypso system, use radio transponders implanted within the prostate. The transponders can emit a radiofrequency of about 10 Hz during radiation treatment delivery. These transponders allow the clinician to track prostate motion real time during an entire treatment session. Real time tracking data has shown that intra-fraction prostate motion can be very significant. See, e.g., Langen K M, Willoughby T R, Meeks S L, et al. Observations on real-time prostate gland motion using electromagnetic tracking. Int J Radiat Oncol Biol Phys 2008; 71:1084-1090. Much like the fiducial markers, these transponders are placed prior to simulation. Once the patient is positioned on the table, these transponders relay positional information real time in 3-D. This data allows the treatment to be interrupted in the event that the transponder falls outside an acceptable range.
Accuracy of the radiotherapy procedure can be limited by uncertainties in the treatment preparation and execution. A conventional way to address these uncertainties in radiotherapy is to surround the clinical target volume (CTV) with a margin to allow for setup uncertainties and movement. This margin should be as small as possible as it increases the volume of normal tissue irradiated and thereby can increase the potential for short-term and long-term side effects to the surrounding tissue. However, many of the current margin models provide generic margin ranges. The models assume that the margins are generally uniform across all patients and all related prostate motion will fall in between these margins during treatment delivery. In addition, these protocols generally do not take into account the patient specific prostate motion.